it's called inflation and making a site, fool.
in 2 years for making the mac port, starting up a company, making plans for the future of GM, and oh, that one little thing, building the freaking site. they're a rather small company. get over it. you've probably already payed anyway, haven't you? and it's not substantial either.
I'm not complaining about the price increase. I'm amused by the amount of stuff they haven't done with that time and investment. Mark, by himself, would have GM8 out by now. You wouldn't have the website, but all that does is run executables with a plugin; hardly an achievement. 64digits, GMG and other sites fulfilled the distribution role quite well anyway.
Also, ENIGMA has managed to do most of a rewrite Game Maker from scratch in the same time, using only a few coders in their spare time.